Why can a poodle and a spaniel breed together but a chicken cannot bread with a goose?

Answer 1

Poodles and spaniels are the same species, despite looking so different. The difference is due to man breeding their ancestors for specific traits.

On the other hand, geese and chickens are barely related. They are both birds, and that's about it.

Answer 2

Poodles and spaniels are the same species, Canis lupus familiaris. All that has happened is that man has bred like with like over hundreds of years, to create offspring that show different characteristics from other breeds.

Chickens and Geese are different species, in fact they share little in common, genetically. They are both birds, but that's where the similarity ends, they aren't even in the same Order. Because they are so genetically dissimilar, they are unable to interbreed.

Two different species can sometimes produce offspring (ligers, mules) but this is not common, and the offspring are usually infertile.

Answer 3

Technically, they may be able to reproduce.

However, their offspring would not be able to produce fertile young, because they would be a hybrid.